The goal of this proposal is to provide a molecular basis for the clinical impact that mutations to cardiac myosin's molecular structure have on patients afflicted with familial hypertrophic cardiomyopathy (FHC). Our approach will take advantage of the transgenic mouse model to express mutant alpha-cardiac and the baculovirus system to express smooth muscle HMMs that have identical signal amino acid substitutions found in FHC patients. This comparative approach, where similar mutations have been genetically engineered into different myosin species, should provide far greater information about presumed key functional domains of the myosin molecule and the consequence of point mutations to these domains. Since the chosen mutations are localized throughout the myosin heavy chain and light chains, we will directly pinpoint crucial intramolecular atomic interactions that are important to myosin's ability to generate force and motion. Using state-of-the-art ultra-compliant microneedle and laser optical trapping techniques in an in vitro motility assay, we will directly measure the force and motion generating capacity of a small myosin ensemble (<50 molecules) and that of a single myosin molecule as it interacts with a single actin filament. These studies will provide the most direct assessment of how FHC point mutations might functionally impact myosin's mechanical performance at the molecular level.